The present invention relates to an apparatus for sequentially changing tools and for holding a tool to be used in a machine tool that uses a plurality of tools.
In general, a plurality of tools are used in the operation of a machine tool. Since the tool operating position is limited, a tool changing operation is inevitably required.
Generally, at least 10 different tools are changed from one to another. In an extreme case, more than 100 different tools must be changed.
A tool holding apparatus, which has heretofore been used, employs an arrangement such as that shown in FIGS. 1(a) and 1(b) of the accompanying drawings. That is, a pull bolt 13, which defines the forward end portion of a tool 1, is clamped by using a collet chuck 32 or a steel ball chuck 33, which is disposed inside a sleeve 31, thereby holding the tool 1. To release the tool 1, it is unclamped by the forward (leftward as viewed in FIG. 1) movement of coned disc springs 36 and a drawbar 35.
Needless to say, the above-described clamping is extremely strong, so that it is impossible to draw the tool 1 from a main spindle 3 by gripping the rear end portion 11 of the tool 1 with an arm 2.
In the prior art, the operation of changing the tool 1 is carried out in the following sequence:
(1) The arm 2, which faces the tool holding apparatus, is rotated to grip the tool 1, which has already been used, at the rear end portion 11. PA1 (2) The drawbar 35 is moved forwardly on the basis of the resilient force from the coned disc springs 36 under the control of a hydraulic cylinder (not shown), thereby releasing the tool 1 from the clamping that has been effected to the pull bolt 13 by the action of the collet chuck 32 or the steel ball chuck 33. PA1 (3) The tool 1 is drawn from the main spindle 3. PA1 (4) The arm 2 is rotated so that a tool 1 which is to be newly used comes to the position of the main spindle 3. PA1 (5) The tool 1, which is to be newly used, is inserted into the main spindle 3 and the magazine. PA1 (6) The drawbar 35 is moved backwardly to allow the collet chuck 32 or the steel ball chuck 33 to clamp the pull bolt 13 of the tool 1. PA1 (7) The arm 2 is made to stop gripping the rear end portion 11 of the tool 1 and then rotated to move away.
The reason why the operation (2) is carried out after the operation (1) is that the tool 1 may fall if it is released from the clamping in the main spindle 3, as in the operation (2), before the arm 2 grips the tool 1 according to the procedure (1).
Further, the reason why the operation (7)is carried out after the operation (6) is that the tool 1 may fall unless the tool 1 is completely clamped by the operation (6) before the rear end portion 11 of the tool 1 is ungripped as stated in (7). Therefore, the arm 2 cannot be released from the tool gripping condition before the tool 1 is satisfactorily clamped.
However, it takes longer in the tool changing operation to carry out the operations (1) and (2), and the operations (6) and (7), serially. As the number of tools 1 which need to be changed increases, the dead time in the machining process unavoidably increases.
It is an object of the present invention to overcome the above-described disadvantage of the prior art and to provide an improved apparatus for holding tools, which makes it possible to simultaneously carry out the steps (1) and (2), and the steps (6) and (7).